US 20070079065 A1
Memory modules address the growing gap between main memory performance and disk drive performance in computational apparatus such as personal computers. Memory modules disclosed herein fill the need for substantially higher storage capacity in end-user add-in memory modules. Such memory modules accelerate the availability of applications, and data for those applications. An exemplary application of such memory modules is as a high capacity consumer memory product that can be used in Hi-Definition video recorders. In various embodiments, memory modules include a volatile memory, a non-volatile memory, and a command interpreter that includes interfaces to the memories and to various busses. The first memory acts as an accelerating buffer for the second memory, and the second memory provides non-volatile backup for the first memory. In some embodiments data transfer from the first memory to the second memory may be interrupted to provide read access to the second memory.
1. A memory module; comprising:
a first memory comprising a first memory type;
a second memory comprising a second memory type; and
a controller coupled to the first memory and the second memory, the controller comprising:
a command interpreter;
a plurality of bus interface controller blocks coupled to the command interpreter;
a first memory controller block, coupled to the command interpreter, for communicating with the first memory; and
a second memory controller block, coupled to the command interpreter, for communicating with the second memory;
wherein the memory module is adapted to physically and electrically couple to a system, receive and store data therefrom, and retrieve and transmit data to the system.
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This non-provisional application claims the benefit of previously filed provisional application 60/690,451; filed 13 Jun. 2005; and entitled “Advanced Dynamic Disk Memory Module”, the entirety of which is hereby incorporated by reference.
The present invention relates generally to a plug and play end-user add-in memory module for computers and consumer electronic devices, and more particularly relates to methods and apparatus for providing additional high performance memory resources for computational or media systems used to accelerate application launch and improve operational performance of application and data sets.
The concept of a RAM based disk substitute has been a part of the Personal Computer (PC) for many years. There are many software programs that set aside blocks of installed main memory for use as a temporary disk partition. The effect of creating such partitions is intended to improve the overall performance of the PC. One advantage of such a product is the increased speed at which a user can access a program or data that is stored in the RAM-based disk partition; However, a drawback of these products is reduced system performance when too much of the main memory is reserved for the RAM-based disk partition. In this case, insufficient scratch pad memory is available to hold the executing program and associated data. This reduction in available main memory forces the PC to use the Hard Disk Drive (HDD) to extend the storage space that it requires to run the application and access the data. This action is commonly referred to as paging.
It is well-known that access performance of a HDD is lower than that of main memory. The performance degradation due to paging to the HDD rapidly overwhelms any performance gain from the use of a RAM-based disk. The performance degradation effects are further compounded in systems that share main memory for integrated graphics solutions (known as Unified Memory Architecture (UMA)). The UMA graphics rely on sharing main memory for the frame buffer and operational scratchpad in a manner similar to that of RAM-based disk products. Systems supporting RAM-based disks and UMA graphics have three sources competing for main memory resources.
Most PC systems offer upgrade options to increase the amount of main memory via, for example, existing extra DRAM memory module connectors on the motherboard. However, these extra connectors are usually difficult to access by the end-user, and in the case of many new systems may not even be available at all.
What is needed is a product and a method for the PC end-user to add low-cost high performance memory to their PC that improves the overall performance of that personal computer with no impact to the main memory resources.
Briefly, a memory module, in accordance with the present invention, provides the functionality of a RAM disk without incurring the main memory performance degradation associated with conventional RAM disks. Various embodiments of the present invention may be added to a system via internal connectors, or may be connected via readily accessible external connectors as is described herein.
Reference herein to “one embodiment”, “an embodiment”, or similar formulations, means that a particular feature, structure, operation, or characteristic described in connection with the embodiment, is included in at least one embodiment of the present invention. Thus, the appearances of such phrases or formulations herein are not necessarily all referring to the same embodiment. Furthermore, various particular features, structures, operations, or characteristics may be combined in any suitable manner in one or more embodiments.
The terms chip, integrated circuit, semiconductor device, and microelectronic device are sometimes used interchangeably in this field. The present invention relates to all of the foregoing as these terms are commonly understood in the field.
System performance of a personal computer (PC) may generally be improved by adding high performance memory. This is usually done by adding main memory or replacing an existing memory module already in the PC with a higher capacity memory module. Embodiments of the present invention typically include high speed memory, such as DRAM, and/or a combination of DRAM and slower writeable non-volatile memory such as FLASH. In the DRAM and FLASH configuration the DRAM acts as a buffer for the FLASH devices. The amount of DRAM and the amount of FLASH on this memory module is configurable at the time of manufacture.
In a further aspect of the invention, the memory module capacity is configurable by the PC to optimize performance for any given usage model. This configuration is called partitioning. A DRAM only configuration for this memory module may be used by the system under certain power conditions and power managed states. It is known that if power is interrupted volatile memory devices lose the integrity of their contents and hence must be reloaded with the appropriate application and data by the driver software or by the operating system. A combination DRAM and FLASH memory module can maintain this information indefinitely in the non-volatile FLASH devices. The applications and data will be maintained during any of the power-managed states including the power-off state of the system. Some examples of those states are full-on, standby, hibernate and power-off. Specialized driver software, or the operating system (OS), is responsible for managing and maintaining coherency of the applications and data stored on this memory module.
In one embodiment of the present invention, the memory module is a hybrid module including DRAM and FLASH memory. This configuration provides a desirable trade-off for a cost-effective high-performance solution in the PC environment. In this configuration the DRAM is used in a number of ways to improve system performance. First a portion of the DRAM space, or all of the DRAM space, can be allocated as a write buffer to the FLASH memory devices. By buffering the write traffic to the FLASH devices in the DRAM, the the DRAM can also used as a read buffer where the most recently used data and applications are temporarily stored. The DRAM in this module allows for the PCI Express bus and the USB bus in the Express Card interface to run at full read and write bandwidths. Without the DRAM, the FLASH devices can sustain only a portion of the available interface read bandwidth and a small portion of the write bandwidth.
The DRAM also plays an important role in reducing the amount of random write traffic to the FLASH memory. Reducing the number of Erase/Write cycles to the FLASH devices is very important in managing the life expectancy of the FLASH memory. FLASH memory has a limited number of Erase/Write cycles before device failure is expected. This is known as FLASH endurance. FLASH endurance is an important parameter when using FLASH as a storage medium in PC systems.
Various memory modules in accordance with the present invention include memory that is used for creating a dedicated RAM-based disk (hereinafter referred to simply as RAM disk) for a personal computer system without consuming main memory resources. Since extra memory is added to the system, the system enjoys a performance advantage without the negative impact caused by consuming main memory to support a RAM disk. Alternatively, such a module may also operate in conjunction with an expandable system bus whereby a plurality of such modules may be installed.
Another issue in using conventional RAM disk is that it relies on the volatile main memory to store the application and or data image. If power is lost, or the system goes through a hard re-boot, the data is lost and the operating system or custom driver is required to restore the memory to a known good state. The re-loading process is often a slow and frustrating event when using a personal computer. Various embodiments of the present invention overcome these problems by including non-volatile and/or semi-volatile memory which substantially reduces or eliminates the problems associated volatile DRAM-based RAM disks at a cost and performance level substantially better than that of FLASH only devices.
The memory hierarchy of
The block diagram of
The block diagram of
Design Attach Point #2 shows ADDMM on the ExpressCard interface. The ExpressCard is an industry standard interface that has a high degree of hardware and software support and is currently defined for PCIe Gen1 and USB 2.0 operation. Some existing disk software infrastructure is lost, as compared to Design Attach Point #1, but some performance enhancements may be gained through improved latency due to locality relative to the CPU on some PC designs.
Design Attach Point #3 shows an ExpressCard or a SATA interface on the North Bridge controller chip. This option shows a location that reduces system latency by eliminating the command transit through the South Bridge. The value this option provides is improved performance through reduced latency, and the opportunity to be used as part of UMA or main memory through software partitions.
Design Attach Point #4 shows a PCI Express interface re-using the Graphics interface port. This gives up to 16 PCIe channels for a substantial bandwidth improvement over a single PCIe and/or 3 to 4 SATA channels. This interface is also one of the lowest latency available in the PC, and exists on almost all present day PCs.
Design Attach Point #5 shows an ExpressCard or SATA interface at the CPU. This eliminates one more level of latency for the ADDMM. The latency through this connection is similar to that of the main memory as there is only one controller in which the requests are routed. It is noted that this attach point does not eliminate the need for main memory since the bandwidth available in main memory is significantly higher than that of the ADDMM.
It is noted that the present invention is not limited to the above-described interfaces, and various embodiments of the present invention may be used with any suitable alternative memory system arrangement or interface.
Three illustrative configurations of the invention, 1) DRAM only; 2) FLASH only; and 3) both DRAM and FLASH; are discussed below.
The DRAM only module-configuration delivers the highest performance for any of illustrative module configurations. A DRAM-only solution has limitations for usage during power-managed states since the DRAM is volatile. The DRAM-only module is not expected to maintain data if power is lost to the memory module unless an auxiliary power source is present. Because the DRAM loses data without an auxiliary power source, it is secure from tampering and secure from data theft when the module is removed from the system. The DRAM-only module may support multiple selectable partitions. Each partition can be treated equally and/or independently depending on usage module and system requirements.
The FLASH-only memory module configuration has better performance than existing USB FLASH drives but does not offer substantial performance benefits. This is not expected to be a typical configuration for the ADDMM, however it is the lowest cost per bit capacity design. Performance of this configuration is expected to improve as FLASH technology improves. The FLASH-only configuration may support multiple partitions.
The DRAM and FLASH combination configuration is a compromise design delivering good performance and high capacity at a market-acceptable price point. This configuration can take full advantage of the ExpressCard interface performance much like the DRAM-only configuration. It has FLASH memory to provide non-volatile storage to better handle power-managed states and to provide adequate capacity. In operation, typical embodiments will not retain data in the DRAM during hibernate and power-off states, and/or in the event of a power loss, unless an auxiliary power backup is provided. The auxiliary power backup, if provided, is preferably sized to allow for the flushing of the DRAM content to FLASH in order to prevent data loss in case of an unplanned power interruption.
The disk drive and memory parameters shown in TABLE 2 highlight differences between solid state memory and hard disk drives with regard to latency and bandwidth. It is noted that the preferred DDR2 type DRAM has bandwidth that is at least 2× that of the presently available interfaces in present PC systems to which it may be connected. It is further noted that various types of FLASH, e.g., the NAND flash memory, has lower read and lower write bandwidth than the presently available interfaces in PCs.
Using simple calculations and adding estimates for controller latency it is apparent that a memory device, that is neither a disk cache nor part of main memory, can add substantial performance to the system. Bandwidth is limited by the interface that is used to add this memory to the system. Available bandwidth also translates into access latency. If the available bandwidth is less than the interface bandwidth then the time it takes for the requested data to be read from, or written to, the memory will increase thus reducing system performance. TABLE 2 outlines the BW available by the different interfaces currently available in the system that is used for the calculation.
Even if there is excessive latency under worst case memory access, assuming 5× worse, which is 1.07 us, the improvement would be >3500× over existing disk drives.
Latency is impacted by the bandwidth of various embodiments. The time it takes to get the data from the memory module into the system adds to the latency of the access. With embodiments having the above-described mix of DRAM and FLASH, the interface will be the performance limiter in presently available systems. As shown in TABLE 2, the preferred DRAM memory has 2× to 3× the bandwidth than the best external interface today can consume with just a single 8 bit wide DRAM device. X16 DRAM devices can deliver 4× to 6× the necessary consumable bandwidth for the interface. This extra available bandwidth is important when looking at the interaction of the DRAM with the interfaces and with the FLASH. The added bandwidth allows the DRAM to concurrently service all available system interfaces to the memory module and the FLASH memory devices as the write buffer to those FLASH devices. The extra available bandwidth from the DRAM devices permits reduction of the operating frequency of the DRAM devices thus making the memory module easier to design, improving the robustness of the memory module design, and typically reducing costs by using the lowest cost DRAM components.
Various embodiments of the present invention include a controller to provide the functionality described herein. The controller functional block diagram in
In one embodiment a display controller block, such as shown in
An illustrative power management controller block, such as shown in
An illustrative DRAM controller block, such as shown in
In some embodiments, an error correction (ECC) engine may be included in the DRAM controller block to ensure data integrity on the memory module. This ECC engine is configured specifically for the DRAM. It detects and corrects data failures caused by soft errors and by hard errors at read time due to a failing memory bit or bits in the DRAM. The failed location information is used to update the available memory location in the memory allocation tables.
The ECC engine operates as shown in
A flash controller block, as shown in
A FLASH read request in a multi-channel FLASH environment departs significantly from access requests to a single channel FLASH read environment.
An ECC engine is also required for the FLASH controller block, as shown in
The functional block that ties the overall controller together is shown in
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As shown in
The first possible action is to return back to idle to wait for another command. This action is taken if the command is determined to not be for the ADDMM memory module or the ADDMM memory module does not recognize it as such. In the event that the command was targeted to the ADDMM memory module and it could not recognize it as a valid request an error response may be initiated by the error handler.
The second possible action is that in certain circumstances the ATA command interpreter will return an error message to the host indicating that the command was targeted towards the correct location but due to some fault it is not able to respond.
The third action is a status request. The ATA command interpreter then looks up the appropriate data from the status registers and or performs a status check and then returns the appropriate status and response to the system. There may be some instances when performing a status check that appropriate status cannot be returned. The request is marked as failed and passed to the error handler. Once past the status check a lookup is performed and the response returned to the host.
The fourth possible action to respond to is a data read request. The read request is passed on to the lookup table where it is determined whether to get the data from the FLASH or from the DRAM. If the data is to be retrieved from the DRAM, then a read command with a length request is sent to the DRAM memory controller and then the data is returned to the host associated with the read request. If the data is to be returned from the FLASH memory, then a command is sent to the FLASH controller with a length of data to retrieve. While retrieving the FLASH data a flag may have been set that would cause the controller to not only stream the data to the host but to also copy that data to the DRAM. If the data is copied to the DRAM, then a CACHE flag is set in the lookup table to direct future accesses for this data to the DRAM. To prevent operational problems if there is a power loss event of any type, the lookup tables keep pointers back to the FLASH memory locations in the event data is needed by the host but cannot be retrieved from the DRAM. This data redundancy is managed for memory space up to the size of the available DRAM. Once the data has been returned to the host and copied to the DRAM, in the event that the DRAM flag was set, the controller will then return to idle and wait for another command. If an error is detected during the lookup, then the error is flagged and passed to the error hander.
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A critical operational element of the memory module controller is how the lookup tables work and how they are managed.
The physical address for the DRAM and each channel of FLASH is managed separately. Because of FLASH specific issues surrounding endurance management and because some of the usage models allow for DRAM to operate independent of the FLASH, each channel of the FLASH device needs to be managed independent of the other. An example of this is shown in
Various embodiments of the present invention support data encryption and digital rights management. Data encryption is primarily handled by the operating system and has minimal impact on embodiments of the invention. In various embodiments digital rights management may conform to industry standard requirements.
The built-in self test (BIST) controller shown in
Embodiments of the present invention find application in PC systems where system performance can be enhanced by adding memory in the PC system memory hierarchy that is substantially better performance than conventional hard disk drives, and better performance than conventional USB FLASH drives.
Embodiments of the present invention can also find application in consumer electronics products where media content (e.g., video, audio) is desired. Examples of such consumer electronics products include, but are not limited to, video camcorders, televisions, personal display devices, gaming consoles and personal gaming devices.
The advantage of some embodiments of the present invention allow for the increased performance of a PC platform, including the reduction of power in a PC platform and the extension of life for the hard disk drives in a PC platform.
It is to be understood that the present invention is not limited to the embodiments described above, but encompasses any and all embodiments within the scope of the subjoined Claims.